Workout motivation is a hot topic these days and, if Instagram, Pinterest, and Facebook are any indication, treat days, finish line medals, and other rewards are the most popular methods. But if you're still not sticking to your goals, you might need fewer "carrots" and more "sticks"—a new study found punishment is more motivating for people than positive reinforcement. Call it 50 Shades of Grey, gym style. (Here's another 22 Ways to Stay Motivated to Lose Weight.)

Researchers from Washington University in St. Louis asked students to play a boring, random computer game, then gave them monetary incentive for answering correctly and a monetary consequence for answering wrong. You'd think gaining money would be a huge motivation, and the scientists did indeed find that both methods helped improve performance. However, punishment was far more effective than reward—two to three times more incentivizing, in fact.

The researchers say this is because people generally fear the pain of having something taken away from them far more than they like the idea of gaining something they don't yet have. "Objectively, you'd think that winning 25 cents would have the same magnitude of effect as losing 25 cents, but that's not what we find," said lead author Jan Kubanek, Ph.D., a postdoctoral research associate at Washington University School of Medicine, in a press release. "Regarding teaching strategies, our study suggests that negative feedback may be more effective than positive feedback at modifying behavior. From an evolutionary perspective, people tend to avoid punishments or dangerous situations. Rewards, on the other hand, have less of a life-threatening impact."

And this motivation hack could work just as well for your workouts. There's a whole field of psychology called operant conditioning that studies exactly what types of punishments and rewards are most effective, explains Ariane Machin, Ph.D., a licensed therapist and sports psychologist at Francis University. The general consensus is that if you're going to use punishment, it's better to use negative types (where something is taken away, like a monetary fine) rather than positive punishment (where something painful is added, like a spanking).

You can put the whips away. When it comes to punishment, a little goes a long way, notes Kubanek. "Punishment does not have to be harsh, since it appears that we tend to react in the same manner to any amount of negative feedback."

To make this work for you, decide what it is that you'd personally hate to lose—like watching Game of Thrones on time so you can gossip about it at the office the next day.

Pass on food or exercise as the punishment, Machin says. "An individual needs to be thoughtful about what they are using as 'punishers' because they don't want to become demoralized or discouraged," she explains. Using meals or workouts as chastisement can form unhealthy associations, making you hate exercise or even spark an eating disorder. Food, Machin explains, can have loaded consequences when it comes to motivation. Just like overrewarding yourself with a 1,000-calorie smoothie after burning 250 calories on the treadmill won't help you reach your goals, forbidding yourself from eating dessert if you don't log all your training miles will just make you resent running.

If you're unsure what to try, Machin suggests taking a page from the researchers' playbook and using the universal motivator: cold, hard cash.

"Gym Pact [an app that either pays you or deducts real money from your account based on completing your scheduled workouts] boasts an 80 percent exercise adherence rate. Money is motivating, thus workouts are more likely to happen because people do not want to lose their money," she explains. (Also try The Best Healthy Living Apps for Weight Loss.) You can also use the tried-and-true dollar in a jar for every time you hit snooze instead of hitting the gym.

But to really make punishments effective, you must combine them with positive reinforcement, Machin adds. The great thing about exercise it that it's already intrinsically rewarding. "As you work up a sweat, you will experience an improved mood from the endorphin rush, increased feelings of competency, and a stronger body. These are all positive things that will increase the likelihood of someone completing the task again," she says. Machin adds that this is why it's so important to pick exercises that you enjoy and that you can do for a lifetime.

So to maximize workout motivation, start by finding an exercise you love (the reward is built right in!) and then hit yourself where it really hurts (like in the wallet or your Netflix queue) if you don't do it. Add in some friends—they're great for providing both a reward and a punishment, Machin points out—and watch your results skyrocket.